1. Field of the Invention
The present invention relates to a sound receiving microphone for a video camera which produces sounds corresponding to the image in the camera and, more particularly, to a sound receiving microphone which provides a sound quality similar to the natural sound by analog audio signal processing.
Korean Patent Application No. 93-1591 is incorporated herein by reference for all purposes.
2. Brief Description of the Prior Art
Generally, in the video camera and recorder (camcorder) purchased by the average consumer for simultaneously recording an image and a sound, the image part of the camcorder includes an optical lens with a zoom function, which lens selectively produces a life-like video image for recording. However, the audio section of the camcorder consists of a general purpose microphone which lacks the capability to produce a life-like sound level. Accordingly, the viewer's visual and aural perception become mis-matched since the visual distance from a camcorder to the subject changes for the image while the sound does not change in correspondence with a change in image size, i.e., with the change in apparent distance between the subject and the camcorder.
In order to overcome this problem, camcorders including a function wherein the audio amplitude changes in proportion to the change in magnification of the zoom lens, i.e., a sound receiving function having a unified image and sound qualities, have been proposed. FIG. 1 is a block diagram showing the sound-receiving microphone of the video camera employing conventional digital audio signal processing.
Referring to FIG. 1, the conventional microphone includes a central (C) microphone 10, a left (L) microphone 11, a right (R) microphone 12, a central amplifier 13, a left amplifier 14, a right amplifier 15, a central electronic volume control 16, a left electronic volume control 17, a right electronic volume control 18, a microcomputer 21, a left mixer 19, and a right mixer 20.
In an attempt to produce a life-like audio output, audio signals input from the left, right and center microphones 10, 11 and 12 are first amplified in C-, L- and R-amplifiers 13, 14 and 15, and the respective output signals are input to respective electronic volume controls 16, 17 and 18. It will be appreciated that the outputs of amplifiers 13, 14, and 15 are adjusted appropriately in C-, L- and R-electronic volume controls 16, 17 and 18 in accordance with a control signal produced by microcomputer 21 and the respective volume-controlled signals are, in turn, provided to L- and R- mixers 19 and 20. Left mixer 19 adds the output of C-electronic volume control 16 to that of L-electronic volume control 17, and amplifies the result. Right mixer 20 adds the output of C-electronic volume control 16 to that of R-electronic volume control 18, and amplifies the result.
It will be noted that microcomputer 21 receives a wide/tele signal, which signal changes depending on the position of the zoom lens in the camera section (not shown), and microcomputer 21 outputs the control signal according to wide/tele signal so as to represent the distance from the sound source. Therefore, the outputs of amplifiers 13, 14 and 15 are input to the relevant electronic volume controls 16, 17 and 18, and are adjusted according to the control signal. Thus, for a wide/tele signal corresponding to the position of the zoom lens in a video part (a camera section which is not shown) of the camcorder, the detected position is indicated by a direct current (DC) voltage and is applied from a camera section (not shown) to microcomputer 21, after being divided into eight steps, i.e., eight steps ranging from A1 to A8 volts.
FIG. 2 shows an embodiment of translating the wide/tele signal into eight steps according to the position of the conventional zoom lens. The output voltage, having one of eight steps and producing a change in the electronic volume associated with the recorded image, can be represented as shown in Table 1.
TABLE 1 ______________________________________ Zoom Lens Voltage VOLUME (in dB) Position (Volts DC) Left Right Center ______________________________________ A0 0.0 0 0 + 1 A1 0.6 - 2 - 2 + 3 A2 1.1 - 4 - 4 + 5 . . . . . . . . . . A8 3.2 - 20 - 20 + 15 ______________________________________
It will be noted that the zoom lens position is divided into eight steps from A1 to A8 depending on the distance, gradually increasing from A0, i.e., the reference and nearest point from the camera, to A8, as shown in FIG. 2. The corresponding wide/tele voltage varies in steps, e.g., 0, 0.6, 1.1 . . . 3.2 volts DC depending on the position of the zoom lens, which then results in the discontinuous change in L and R electronic volume controls 17 and 18, e.g., 0, -2, -4, . . . -20 dB and an attendant discontinuous change in C-electronic volume control 16, e.g., 1, 3, 5 . . . 15 dB. The central audio input signal is increased when the position of the zoom lens in FIG. 2 goes from "wide" to "tele" (which means that the distance received to the subject is shortened) while the level of central audio input signal is decreased when the position of the zoom lens in FIG. 2 goes from "tele" to "wide" (which means that the distance to the subject is decreased). For example, the human voice is loud when the position of the zoom lens goes from "wide" to "tele" and is soft when the position of the zoom lens goes from "tele" to "wide". Since the value of the electronic volume method is fixed to eight discrete steps, e.g., the sound feels discontinuous when the sound changes to match a change in lens position. In addition, since the microcomputer 21 is needed for control of the electronic volume operation, the manufacturing cost of the camcorder is high.